1. Field of the Invention
The present invention relates to an automatic sheet feeding apparatus of reversible roller type for separating and feeding originals or recording sheets one by one in a facsimile, copying machine, printer and the like.
2. Related Background Art
In the past, sheet feeding apparatuses which comprise a separation roller rotated in a sheet feeding direction, and a reversible roller urged against the separation roller and wherein stacked sheets are separated and fed out one by one are already known.
Normally, in such an automatic sheet feeding apparatus of reversible roller type, a torque limiter is arranged in a drive mechanism for the reversible roller so that, when a plurality of sheets are pinched between the separation roller and the reversible roller, the reversible roller is rotated in a reverse direction to return sheets other than a sheet to be fed forwardly back, and, when a single sheet is pinched between the separation roller and the reversible roller, the drive connection to the reversible roller is interrupted by the torque limiter, thereby rotating the reversible roller by the rotation of the separation roller.
In the automatic sheet feeding apparatus having the reversible roller of this kind, as disclosed in U.S. Pat. No. 4,368,881 and the like, when a driving force is applied to the reversible roller, the force acts in a direction that the reversible roller is urged against the separation roller. With this arrangement, since the urging force between the separation roller and the reversible roller can be automatically adjusted in response to the strength of a limit value of the torque limiter, the separating ability and feeding ability for the sheet are stabilized. That is to say, even when the limit value of the torque limiter becomes greater than a setting value due to the dispersion in the manufacture of the torque limiter, since the urging force between the separation roller and the reversible roller is also automatically increased to increase the separating force for the sheets, the separating ability is not worsened, thus providing the stable sheet separation.
However, in the sheet feeding apparatus wherein the urging force is automatically adjusted, the following problems arise.
That is to say, in such sheet feeding apparatus, when the driving force is applied to the reversible roller, not only the force acts in the direction that the reversible roller is urged against the separation roller, but also a force generated by a friction between the reversible roller and the separation roller acts in a direction that the reversible roller is urged against the separation roller. Thus, when the limit value of the torque limiter becomes greater than the setting value, the urging force tends to become too great. If the urging force is too great, a braking force of the sheet increases considerably, with the result that a feed roller disposed at a downstream side of a separating station is subjected to be greater load, thereby causing the poor feeding (slip) due to the less feeding force of the feeding roller.
The most simple conventional way to solve this problem is that the feeding force of the feed roller is previously set to have a value greater enough to the expected maximum load to be applied thereto. In this case, however, since the torque margin must be estimated excessively in consideration of the maximum sliding friction acting on bearings supporting roller shafts, the manufacturing cost of the apparatus is increased.
The present invention aims to solve these conventional problems.